1. Field of the Invention
The present invention generally relates to cryopumps and regenerating methods of the cryopumps. More particularly, the present invention relates to a cryopump configured to implement a regenerating process by reverse-operating a cryogenic cooler and a regenerating method of the cryopump.
2. Description of the Related Art
In semiconductor manufacturing equipment, for example, it is necessary to realize a high vacuum state. Accordingly, cryopumps are frequently used as vacuum pumps for realizing the high vacuum state. The cryopump requires a cryogenic cooler in the principle of vacuum production. As the cryogenic cooler used for the cryopump, a Gifford McMahon cycle type cryogenic cooler (hereinafter “GM-type cryogenic cooler”) is known.
The GM-type cryogenic cooler and a cryopanel or the like provided in a pump housing are thermally connected to each other. In a cooling process, a gaseous substance in the pump housing is condensed and absorbed into the cryopanel or the like, so that the high vacuum state can be realized.
Regenerating is required for the cryopump having the above-mentioned structure. Regenerating is a process wherein heat is applied to the gaseous substance condensed and absorbed into the cryopanel or the like in the cooling process so that the temperature is increased and the substance is liquefied and boiled to become gas again so as to be discharged outside of a pump vessel.
Therefore, in the regenerating process, it is necessary to heat (raise the temperature) of the cryopanel or a stage of the GM-type cryogenic cooler thermally connected to the cryopanel. As a method for raising the temperature, for example, a method discussed in Japanese Patent No. 2567369 is known.
In the method discussed in Japanese Patent No. 2567369, a temperature rising cycle is realized by reversing a cooling cycle of the cryogenic cooler and the cryogenic cooler itself is used as a heat source.
In this method, a motor for reciprocally moving a displacer in a cylinder via a crank mechanism is rotated in a reverse direction. In addition, the operational timing of a valve is changed 180 degrees compared to an operation for a cooling cycle, so that the cooling cycle is reversed and a temperature rising cycle is conducted by operating the cryogenic cooler as heat generation means. This heat generation means does not require special equipment and only reversing the cooling cycle is required. Therefore, its structure is simple and convenient.
FIG. 1 is a structural view of a related art cryopump. More specifically, FIG. 1 shows a cryopump 1 which realizes a temperature rising cycle by reversing a cooling cycle of a cryogenic cooler.
The cryopump 1 is attached to a process chamber not shown in FIG. 1, such as a semiconductor manufacturing apparatus. The cryopump 1 evacuates the inside of the process chamber. The cryopump 1 includes a compressor 1, a vacuum vessel 4, a cryogenic cooler 5, a shield 9, a cryopanel 10, a controller 17, and others.
A compressor 3 raises the temperature of coolant gas such as helium gas so as to transfer the gas to the cryogenic cooler 5. In addition, the compressor 3 receives coolant gas that is adiabatically expanded by the cryogenic cooler 5 so as to raise the temperature of coolant gas again.
The vacuum vessel 4 is attached to the above-mentioned process chamber. The cryogenic cooler 5, the cryopanel 10, and others are provided in the process chamber. A gate valve not shown in FIG. 1 is provided between the vacuum vessel 4 and the process chamber. By closing the gate valve, the vacuum vessel 4 is isolated from the process chamber in an airtight manner.
The cryogenic cooler 5 is a GM-type cryogenic cooler. The cryogenic cooler 5 includes a first stage cylinder 14, a second stage cylinder 15, a reversible motor 16, and others.
A first stage displacer 14A is provided inside the first stage cylinder 14 so as to reciprocally move in upper and lower directions in FIG. 1. In addition, a second stage displacer 15A is provided inside the second stage cylinder 15 so as to reciprocally move in upper and lower directions in FIG. 1.
The first stage displacer 14A and the second stage displacer 15A are connected to each other and reciprocally move inside the cylinders 14 and 15 by using the reversible motor 16 as a driving source.
In addition, a first stage expansion room is formed between the first stage cylinder 14 and the first stage displacer 14A. A second stage expansion room is formed between the second stage cylinder 15 and the second stage displacer 15A. Volumes of the first stage expansion room and the second stage expansion room are changed by reciprocal moving of the displacers 14A and 15A.
The reversible motor 16 can be rotated in a forward direction and in a reverse direction. The reversible motor 16 is connected to the controller 17. Following instructions from the controller 17, rotation in the forward direction or the reverse direction can be selected.
A first stage cooling stage 7 is provided around an external periphery of the first stage cylinder 14. In addition, a shield 9 as a first cryopanel is provided at the first stage cooling stage 7. The shield 9 prevents outside heat from being transferred to the cryopanel 10.
Furthermore, a louver 12 is provided at the shield 9 so as to be positioned in the vicinity of an upper part opening of the vacuum vessel 4.
A second stage cooling stage 8 is provided around an external periphery of the second stage cylinder 15. In addition, the cryopanel 10 as a second cryopanel is provided at the second stage cooling stage 8. Activated carbon 11 is provided in the cryopanel 10.
In the cryopump having the above-mentioned structure, when a vacuum process is implemented, the controller 17 rotates the reversible motor 16 in the forward direction. Because of this, the cryogenic cooler 5 is in a cooling mode so that the coolant gas supplied from the compressor 3 to the first stage expansion room and the second stage expansion room is adiabatically expanded as the displacers 14A and 15A move and thereby a cold state is generated.
As a result of this, the first stage cooling stage 7 is cooled at, for example, approximately 30 through 100 K, and the shield 9 is cooled at, for example, a temperature equal to or less than approximately 100 K. In addition, the second stage cooling stage 8 is cooled at, for example, approximately 4 through 20 K, and the cryopanel 10 is cooled at, for example, a temperature equal to or less than approximately 20 K.
Gaseous substances in the process chamber enter from the opening of the upper part into the vacuum vessel 4. Water or carbon dioxide is condensed by mainly the louver 12 and the shield 9. Argon and nitrogen are condensed by mainly the cryopanel 10. Hydrogen, neon, helium, and others are absorbed by mainly the activated carbon 11. Thus, the process chamber is evacuated so that the high vacuum state can be realized.
As discussed above, a gas substance such as argon discharged from inside the process chamber is condensed or absorbed by the shield 9, the cryopanel 10, and the activated carbon 11. Therefore, as the amount of the condensed or absorbed substance is increased, a discharging ability of the cryopump 1 is degraded. Because of this, as discussed above, the regenerating process for discharging substances condensed or absorbed by the cryopump 1 is required.
Next, the regenerating process of the related art cryopump 1 is discussed.
In the regenerating process discussed below, the reversible motor 16 is rotated in the reverse direction so that the cooling cycle of the cryogenic cooler 5 is reversed. By reversing the cooling cycle of the cryogenic cooler 5, the coolant gas is adiabatically compressed in the first stage expansion room and the second stage expansion room, so that adiabatic compression heat is generated.
Temperatures of the shield 9 and the cryopanel are raised by the adiabatic compression heat via the cylinders 14 and 15 and the cooling stages 7 and 8 so that the regenerating process is implemented.
FIG. 2 is a flowchart indicating a regenerating process implemented by the controller 17 in the related art.
In the process shown in FIG. 2, the regenerating process is implemented based on temperature of the first stage cooling stage 7. Because of this, a first stage temperature sensor 18 is provided at the first stage cooling stage 7. The temperature of the first stage cooling stage 7 detected by the first stage temperature sensor 18 is sent to the controller 17.
When the regenerating process shown in FIG. 2 is started, the controller 17 rotates the reversible motor 16 in a reverse direction in step S10. Because of this, the mode of the cryogenic cooler 5 is switched from the cooling mode to the regenerating mode, so that, as discussed above, the coolant gas is adiabatically compressed in the first stage expansion room and the second stage expansion room and thereby the adiabatic compression heat is generated.
Temperatures of the shield 9 and the cryopanel are raised by the adiabatic compression heat via the cylinders 14 and 15 and the cooling stages 7 and 8 so that the regenerating process is implemented.
At this time, purge gas such as nitrogen gas is introduced in the vacuum vessel 4 and substance such as argon, returned to a gaseous state by the regenerating process together with the purge gas are discharged from the vacuum vessel 4.
In step S11, whether temperature T1 of the first stage cooling stage 7 detected by the first stage temperature sensor 18 becomes a target temperature for regenerating is determined. By the process in step S11, rotation in the reverse direction of the reversible motor 16 continues until the temperature T1 of the first stage cooling stage 7 detected by the first stage temperature sensor 18 becomes the target temperature.
When the temperature T1 of the first stage cooling stage 7 is determined to become the target temperature in step S11, the process goes to step S12 so that the controller 17 switches the mode of the cryopump 1 to a temperature control mode. In this temperature control mode, the rotational speed of the reversible motor 16 is decreased and supply of the purge gas is stopped.
However, in the cryopump 1 where the cooling cycle of the cryogenic cooler is reversed by rotating the reversible motor 16 in the reverse direction so that the regenerating process is implemented, it is not possible to control rising temperatures of the first stage cooling stage 7 and the second stage cooling stage 8 independently.
In other words, compression expansion heat generated in the first and second expansion rooms is proportional to expansion volumes of the first and second stage cylinders.
The diameter of the first stage cylinder 14 is larger than the diameter of the second stage cylinder 15. The stroke amount of the first stage displacer 14A is equal to the stroke amount of the second stage displacer 15A. Because of this, the volume of the first stage expansion room is larger than the volume of the second stage expansion room. Therefore, a temperature rising rate of the first stage cooling stage 7 at the time of regenerating is greater than a temperature rising rate of the second stage cooling stage 8.
Details of this are discussed with reference to FIG. 3. Here, FIG. 3 is a graph showing temperature changes of the first stage cooling stage 7 and the second stage cooling stage 8 when a regenerating process is controlled based on the temperature detected by a first stage temperature sensor.
A solid line shows temperature change characteristic of the first stage cooling stage 7. A one point dotted line shows a temperature change characteristic of the second stage cooling stage 8. In addition, the graph shown in FIG. 3 shows an example where the regenerating process is controlled based on the temperature detected by the first stage temperature sensor 18 provided at the first stage cooling stage 7 discussed with reference to FIG. 2.
In rising temperature, when the rotational speed of the reversible motor 16 is adjusted by the temperatures detected by the first stage cooling stage 7 and the second stage cooling stage 8, the rotation speed of the reversible motor 16 may have to be frequently changed.
However, in the actual cryogenic cooler, the rotational speed cannot be frequently changed due to the characteristic of the reversible motor 16.
In the related art, the regenerating process is controlled based on only the temperature detected by the first stage temperature sensor 18 provided at the first stage cooling stage 7. Therefore, the mode is switched to the temperature control mode when the temperature of the first stage cooling stage 7 reaches the target temperature so that the rotation speed of the reversible motor 16 is decreased.
Because of this, at the time t1 when the temperature of the first stage cooling stage 7 reaches the target temperature T1, the temperature of the second stage cooling stage 8 has not reached the target temperature T2. Hence, after the temperature of the second stage cooling stage 8 reaches the target temperature T2 in the temperature control mode, the rotation in the reverse direction of the reversible motor 16 is completely stopped so that the regenerating process is finished.
However, in this regenerating method, while the temperature of the first stage cooling stage 7 reaches the target temperature T1 at the time t1, the temperature of the second stage cooling stage 8 reaches the target temperature T2 at the time t2.
Thus, it takes time Δt for the temperature of the second stage cooling stage 8 to reach the target temperature T2 after the temperature of the first stage cooling stage 7 reaches the target temperature T1. Hence, in the related art, the regenerating process takes a long time.
FIG. 4 is a graph showing temperature changes of the first stage cooling stage 7 and the second stage cooling stage 8 when a regenerating process is controlled based on the temperature detected by a second stage temperature sensor provided at the second stage cooling stage 8.
The horizontal axis of the graph indicates time and the vertical axis of the graph indicates temperature.
A solid line shows the temperature change characteristic of the first stage cooling stage 7. A one point dotted line shows the temperature change characteristic of the second stage cooling stage 8.
In the regenerating method shown in FIG. 4, when the temperature of the second stage cooling stage 8 reaches the target temperature T2, the rotation of the reversible motor 16 is stopped and thereby the regenerating process is stopped.
In this method, since a time period during which the temperature of the second stage cooling stage 8 reaches the target temperature T2 can be shortened, time difference (Δt) between the time t1 when the temperature of the first stage cooling stage 7 reaches the target temperature T1 and the time t2 when the temperature of the second stage cooling stage 8 reaches the target temperature T2 can be shortened.
However, as discussed above, a temperature rising rate of the first stage cooling stage 7 at the time of regenerating is different from a temperature rising rate of the second stage cooling stage 8.
Therefore, the temperature of the first stage cooling stage 7 reaches the target temperature T1 before the temperature of the second stage cooling stage 8 reaches the target temperature T2. Rising temperature continues even after the time t1. Hence, in the first stage cooling stage 7, excess temperature rising indicated by an arrow ΔT occurs.
Because of this, the temperature of the first stage cooling stage 7 exceeds a reliability limiting (critical) temperature before the temperature of the second stage cooling stage 8 reaches the target temperature T2. Rising temperature continues even after the time t1, so that a problem may occur.